Contamination of human blood and blood components with pathogens such as human immunovirus (HIV), hepatitis and/or bacteria create a serious risk for patients who receive blood or blood components via blood transfusions.
To help combat the problem of pathogenic contamination in blood and/or blood components, one method of reducing pathogens in blood and biologically useful fluids may be to use radiation to substantially destroy any pathogens contained in the fluid. Radiation may be used to inactivate pathogens contained in blood and blood components by generating mutagenic alterations in their genetic material. Above a minimum dose of radiation, the pathogens lose their capacity to reproduce. Radiation damages the nucleic acids of the pathogens by creating intrastrand nicks and inducing nucleotide photodimerization, both of which disrupt nucleic acid replication. Through such mechanisms, irradiating blood and blood components with either visible or ultraviolet (UV) light can be an effective means for reducing undesirable pathogens within blood and other biologically useful fluids.
Unfortunately, the energy of short wavelength UV light may also damage the blood and blood components that are the desired end-products of the irradiation process. Thus, an inherent problem in the application of UV-irradiation techniques is controlling the irradiation of the fluid so as to ensure sufficient radiation exposure to reduce undesirable pathogens within a fluid while at the same time minimizing or eliminating damage to the biologically useful fluids. One way to avoid substantial damage to the biologically useful fluid by UV light is to design an apparatus which will effectively mix the fluid in such as way so as not to over-expose the fluid to the radiation.
Blood and blood components can also be decontaminated using pathogen reducing agents or photosensitizers which, when activated, also reduce pathogens contained in the blood or other biologically useful fluids but does not destroy the biological activity of the blood or blood component product.
Pathogen reduction agents, which may be used with this invention, include the class of photosensitizers known in the art to be useful for reducing pathogens. A “photosensitizer” as defined here is any compound which absorbs radiation of one or more defined wavelengths and subsequently transfers the absorbed energy to an energy acceptor. Thus, such photosensitizers may be activated by the application of electromagnetic spectra (e.g., UV and visible light) to then reduce certain pathogens with which they may interact.
Various photosensitizers have been proposed for use as blood or blood component additives to inactivate pathogens in body fluids. Examples of non-endogenous photosensitizers that have been proposed for use as blood or blood component additives include porphyrins, psoralens, acridines, toluidines, flavins (acriflavin hydrochloride), phenothiazine derivatives, coumarins, quinolines, quinones, anthroquinones and dyes such as neutral red and methylene blue.
Other categories of photosensitizers are endogenous pathogen reduction agents, such as 7,8,10-trimethylisoalloxazine (lumiflavin), 7,8-dimethylalloxazine (lumichrome), isoalloxazine-adenine dinucleotide (flavin adenine dinucleotide [FAD]), alloxazine mononucleotide (flavin mononucleotide [FMN] and riboflavin-5-phosphate), vitamin K and vitamin L and their metabolites and precursors, napththoquinones, naphthalenes and naphthols as well as their derivatives. One preferred example of an endogenous photosensitizer contemplated for use with this invention is an alloxazine such as 7,8-dimethyl-10-ribityl isoalloxazine, commonly known as riboflavin. An advantage of using endogenous photosensitizers to reduce blood contaminants is that endogenous photosensitizers are not inherently toxic to the blood cells and if photoactivated do not yield toxic photoproducts after exposure to radiation. Therefore, a removal or purification step is not required after the decontamination process, and the treated product can then be stored in the same solution used in the pathogen reduction process, transfused into a patient, or returned directly to the donor.
One method of decontaminating blood or blood components using a photosensitizer includes mixing an effective amount of a photosensitizer with the fluid to be decontaminated in a batch-wise way; then exposing the fluid to an amount of photoradiation at an appropriate wavelength sufficient to activate the photosensitizer and allow the activated agent to interfere with the pathogens contained within the fluid such that the pathogens contained in the fluid are reduced. The wavelength of light used will depend on the photosensitizing agent selected as well as the type of blood components being pathogen reduced. The light source or sources may provide light in the visible range, the ultraviolet range, or a mixture of light in both the visible and the ultraviolet range
Decontamination or pathogen reduction systems may be designed as stand-alone units as described above, or may be incorporated into existing apparatuses known to the art for separating or treating blood to be withdrawn from or administered to a patient. For example, such blood-handling apparatuses include the COBE Spectra™ or TRIMA® apheresis systems, available from Gambro BCT Inc., Lakewood, Colo., as well as apheresis systems of other manufactures. The decontamination system may be inserted before the collected blood is separated into components. Alternatively, the decontamination system may be inserted downstream of the point where the blood is separated and/or collected, or at any point after separation of blood constituents. It may even be inserted just prior to reinfusion of the blood product back into the patient. It is further understood that discrete irradiation sources could be placed upstream from the collection points of each separated blood component, such as red blood cells, platelets, and plasma. The use of three separate blood decontamination systems, one for each separated blood component, may be preferred to placement of a single blood decontamination system upstream of the blood separation vessel of an apheresis system because the lower flow rates in the separated component lines may allow for greater ease of irradiation.
In other embodiments, decontamination systems for use in and/or with the present invention may be used to process previously collected and/or stored blood products, whole blood or components, in a batch-wise way, as discussed above, and in further detail below. In some photosensitizer methods, the blood product to be decontaminated is flowed through an entry port into a photopermeable bag or other container. The term “photopermeable” means that the material of the container is adequately transparent to photoradiation.
Polymeric bags and like containers, flexible or otherwise, which are commonly used to collect and store blood and blood components, are useful as the photopermeable containers referred to above.
After the pathogen reduction process, the pathogen reduced fluid may then be flowed out of the photopermeable container into a storage container through an exit port, or may be stored in the same photopermeable container used in the photoinactivation process until transfused into a patient.
One problem with the use of light alone or light in combination with a photosensitizer to reduce pathogens in blood or blood products, is that during the pathogen reduction process, a portion of the fluid to be pathogen reduced may become trapped within dead spaces or opaque portions of the bag or container. Fluid trapped in these dead spaces or opaque portions may not be reached by light and may therefore still contain pathogens which will re-infect the fluid which was previously pathogen reduced.
Another problem in pathogen reducing fluid using light results from the laminar nature of fluid flow in a container. In either a flow-through or a batch wise system, a parabolic velocity profile exists for the fluid contained in either the fluid-flow channel or a self contained bag. Upon agitation or application of a force, the fluid at the center of the flow channel or bag is traveling at a maximum velocity, while the fluid close to the walls at the bag-fluid interface remains nearly stationary. Because of this flow profile, upon irradiation of blood or blood components, the exposure time of the blood is the shortest for the blood traveling at maximum velocity at the center of the container, and increases for successive portions of the flow profile moving outwardly from the center. Therefore, not all of the blood in a bag is irradiated at the same intensity and for the same length of time. In addition to the velocity profile, blood tends to spread in a thin film along the surface of the bag due to surface tension and the tendency of blood to cling to the bag's surface. In the absence of vigorous agitation, the blood located along the walls of the container would have an extremely long residence time. Thus, the blood or blood component nearest the walls (closest to the irradiation source) runs the risk of being overexposed to radiation which may significantly damage the blood or blood components, while the fluid in the middle of the container runs the risk of being under irradiated, thus any pathogens contained in this region would receive little or no radiation, and would be likely to re-contaminate the fluid with still viable pathogens.
In view of the above background, it can be seen that there is a need for a method and apparatus for pathogen reducing a fluid that ensures adequate exposure of all of the fluid to radiation while simultaneously minimizing the damage to the blood or blood components.